1. Field of the Invention
The present invention relates generally to compositions used to encapsulate electronic devices. More particularly, the present invention relates to flexible epoxy compositions for use as encapsulants, which are designed to provide thermal and hydrolytic stability.
2. Description of the Background Art
In the fabrication of electronic devices and circuits, the electronic devices are protected from the adverse effects of the environment by filling the empty spaces between components on the device with a potting material which encapsulates these components. The electronic device must be protected from contact with anything in the environment, such as water or other contaminants, which would produce electrical shorting in the device. If the electronic device is used outdoors, such as in automotive, aircraft, marine, or building applications, the potting or encapsulant material must be stable enough to provide protection over extreme outdoor temperatures and humidity conditions. At elevated temperatures, the encapsulant material could liquefy, crack, shrink, expand, or become electrically conductive, any one of which would allow water or other contaminants to contact the device and produce short circuits. When the encapsulant is exposed to moisture, such as from humid air, the temperature at which the encapsulant breaks down is even lower. Consequently, such encapsulants must possess both thermal stability and hydrolytic stability.
Epoxy compounds have been widely used as adhesives, encapsulants and coatings for a variety of applications. Epoxy compounds typically have good insulating properties and excellent adhesion, and are easy to process. However, flexibilized epoxies usually have poor thermal stability, hydrolytic stability and mechanical properties; and consequently, have not been used for elastomeric applications. Rather, polyurethane or silicone potting compositions have been used for these applications. However, polyurethanes are more difficult to process due to their tendency to foam when in contact with moisture--containing surfaces. Silicones have the disadvantage of being poor adhesives and are also mechanically weak and costly.
Thus, a need exists in the electronics industry for a potting or encapsulant composition which provides thermal and hydrolytic stability while at the same time providing good insulation, good adhesion and good processing characteristics.